Method for forming fine multilayer resist patterns

ABSTRACT

Fine resist patterns having high sensitivity and steeply improved residual film ratio is obtained by forming a multilayer film consisting of organic substances on a substrate, making at least one layer other than the lowest layer of said multilayer film contain metal elements, irradiating said multilayer film with light or radiations, and developing with plasma.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for forming fine resistpatterns, in particular, a method for forming fine resist patterns tosemiconductors, ICs, bubble memories and the like by performing a dryresist development process.

2. Description of the Prior Art

Hitherto for the formation of fine resist patterns to semiconductors,the following steps have been carried out:

(a) A resist prepared by dissolving an organic high-polymer in a solventis spin-coated on the substrate.

(b) The coated film is dried.

(c) The dried film is exposed to light or radiations such as electronbeam, X-rays, α-rays, or ion beams.

(d) A pattern is formed by a wet development process utilizing thedifference of solubility to a solvent between the part exposed to lightor radiations and the part not exposed.

However, the above mentioned method have some problems that a largeamount of solvent is required; in the course of forming a pattern bydevelopment the pattern swells with the solvent to spoil the dimensionalaccuracy; the sensitivity of resist itself is made not uniform; and thesensitivity lowers due to a change with the passage of time.

Besides, the dry lithography is known, which prepares a resist film byplasma polymerization and forms a resist pattern by oxygen plasmadevelopment (J. Appl. Phys. vol. 51, p. 3938, 1980).

However, in the above mentioned method the sensitivity has been poor andthe ratio of film thickness of the part remaining as a pattern after thedevelopment to the film thickness before the development (hereaftercalled the residual film ratio) is in the extent of 10 to 15%, at best50 to 60%, so that it has been difficult to obtain a film thicknessbearable to the subsequent selective etching (Japanese Patent Laid-openNo. 72175/'77).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for formingfine patterns having high sensitivity and steeply improved residual filmratio.

The object of the present invention has been attained by making an upperlayer of a substance having a low rate of plasma development and a lowerlayer of a substance having a high rate of plasma development, anddeveloping with plasma to form fine patterns. More particularly, saidupper layer is formed by dissolving in a solvent at least one compoundselected from organosilicon high polymers, organosilicon compounds,organoaluminum compounds, organotin compounds, and organolead compoundswith other organic high polymers than said organosilicon high polymersto form a solution; and applying the solution on the lower layer to forma coated film. Said upper layer may be formed by a plasma polymerizationcaused by generating a plasma discharge in a mixed atomosphere of atleast one compound selected from organosilicon compounds with at leastone monomers described below. Thereafter the upper layer is subjected toa plasma development.

The further improvement of the sensitivity can be attained by adding tothe above mentioned solution at least one compounds selected fromhalogen containing high polymers, epoxy group containing highpolymersand sulfone group containing high polymers or to the above mentionedplasma discharge atmosphere at least one compound selected from halogensubstituted styrenes and epoxy compounds.

It is considered that the low rate of plasma development of said upperlayer results from the generation of oxides such as SiO₂, A1₂ O₃, SnO₂or PbO in the film when exposed to oxygen plasma.

On the other hand, if the thickness of upper layer is thinner than thelower layer, the residual film ratio is more improved.

The materials and manufacturing processes used in the present inventionare explained as below.

First, in the resist film forming step in FIG. 1, as seen in FIG. 2, ona substrate 1 of a silicon wafer or a chrome coated glass is formed anorganic thin film 2 having a thickness of 0.5 to 2 μm, and furtherthereon an organic thin film 3 having a thickness of 0.01 to 0.2 μm andcontaining Si, Al and the like is formed to produce a multilayer resist10. The thin film forming method may be spinner coating, while theplasma polymerization process can provide an uniform film thickness andreduce defects such as pin holes.

This resist film 10 is exposed to light or radiations 7. Then it isdeveloped with a plasma containing fluorine and subjected to the plasmadevelopment step of upper layer of FIG. 1 to form the pattern of thinfilm 3 shown in FIG. 2 as B or B'.

Thereafter the plasma development of lower layer of FIG. 1 is done witha plasma containing oxygen to erode away the exposed part of thin film 2and obtain the resist pattern shown in FIG. 2 as C or C'.

A heating step at 100° to 200° C. may be inserted between the exposureand the plasma development of upper layer steps.

For the lower layer of resist layer is desirable the materials able tobe developed with oxygen plasma. Concretely the lower layer is formed bydissolving at least one high polymer compound selected from thecompounds (a) to (d) in a solvent to form a solution, applying thesolution on the substrate by spin-coating and drying:

(a) polystyrene, polychlorostyrene, poly-α-methylstyrene,polychloromethylstyrene, brominated polystyrene, iodinated polystyreneand other polystyrene derivatives;

(b) poly(methyl methacrylate), poly(ethyl methacrylate), poly(propylmethacrylate), poly(butyl methacrylate), poly(phenyl methacrylate),poly(methyl acrylate), poly(vinyl acetate), poly(methyl vinyl ketone),poly(methyl isopropenyl ketone), poly(phenyl isopropenyl ketone),phenolic resin, polyester, polyether, epoxy resin and other oxygencontaining highpolymers;

(c) polysulfon, polysulfide and other sulfur containing highpolymers;

(d) polyamide, polyimide, polyacrylonitrile, polymethacrylonitrile andother nitrogen containing highpolymers.

The lower layer can be formed by plasma polymerization of at least onemonomers selected from the compounds (e) to (i).

(e) ethylene, propylene, butene, butadiene, isoprene, and otherhydrocarbons;

(f) vinyl chloride, vinylidene chloride, chloroprene, vinylidenefluoride, tetrafluoroethylene, trichloroethylene, tetrachloroethyleneand other halogenated hydrocarbons;

(g) styrene, chlorostyrene, α-methylstyrene, chloromethylstyrene,brominated styrene, iodinated styrene and other styrene derivatives;

(h) methyl methacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, phenyl methacrylate, methyl acrylate, vinyl acetate,methyl vinyl ketone, methyl isopropenyl ketone, phenyl isopropyl ketone,phenols, ester compounds, ether compounds, epoxy compounds and otheroxygen containing compounds;

(i) amides, imides, acrylonitrile, methacrylonitrile and other nitrogencontaining compounds.

Preferably the lower layer is formed by spin-oating and drying asolution of polystyrene, phenol resin or polyimide in solvent or byplasma polymerizing styrene, phenol or imide monomer.

The upper layer of the resist layer is formed by applying the followingmixture (j), if necessary adding solvent, by means of spin-coating anddrying:

(j) a mixture of at least one compounds selected from (i) organosiliconhigh polymers such as polydimethsiloxane, polyvinyltrimethylsilane,polymethacryloxytrimethylsilane and (ii) organosilicon compoundsselected from silane compounds such as tetramethylsilane,tetravinylsilane, tetramethoxysilane, methyltriethylsilane, siloxanessuch as hexamethyldisiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane,silazanes such as hexamethyldisilazane, and (iii) organometalliccompounds such as trimethyl aluminium, triethyl aluminum, tetramethyltin, tetraethyl tin, tetramethyl lead, and tetraethyl lead with at leastone compound selected from high polymers mentioned in said (a) to (d).

Besides, the upper layer is formed by plasma polymerization of thefollowing mixture (k).

(k) a mixture of at least one organosilicon compounds selected fromsilane compounds such as tetramethylsilane, tetravinylsilane,vinyltrimethylsilane, divinyldimethylsilane, trivinylmethylsilane,diallyldimethylsilane, tetraethylsilane, tetramethoxysilane,vinyltrimethoxysilane and methyltriethylsilane; siloxanes such ashexamethyldisiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane; andsilazanes such as hexamethylsilazane with at least one monomer selectedfrom the above mentioned (e) to (i).

In order to improve the sensitivity of upper layer of the resist layerthe abovementioned solution of (j) is mixed with at least one highpolymers compound selected from the compounds described in following (i)to (iii):

(i) polychloromethylstyrene, iodinated polystyrene and other halogencontaining high polymers;

(ii) poly(glycidyl methacrylate), epoxidated polybutadiene and otherepoxy group containing high polymers;

(iii) polyolefinsulfon and other sulfon group containing high polymers.

Besides, the mixture of (k) may be mixed with at least one compoundselected from chloromethylstyrene, iodinated styrene, butadienemonoxide, glycidyl methacrylate, allylglycidyl ether, epichlorohydrinand epibromohydrin, and then subjected to a plasma discharge to causeplasma polymerization.

Next, a description is made in regard to the plasma polymerization. Forthe aforementioned plasma polymerization are employed the apparatuses ofhigh-frequency discharge type, microwave discharge type and separativetype in which the discharge part and the polymerization part areseparated. These plasma generating apparatuses give little damage to thesubstrate surface. The electric power of discharge is less than 50 W,desirably 1 to 20 W. The discharge power less than 50 W can not causedecomposition of epoxy groups.

For the plasma development are employed the plasma-generators ofparallel plate electrode type (or diode type), barrel type,high-frequency inductive coupling type, and microwave discharge type.The electric power of discharge ordinarily is 100 to 300 W, and the gaspressure is 0.01 to 0.5 Torr. If the plasma development is carried outusing a parallel plate electrode type plasma generator under theelectric power of discharge of 100 to 300 W and the gas pressure of 0.1Torr or the extent, the development accuracy is more improved.

The gas used for the plasma development of upper layer of said resistlayer is a mixture of one kind of gas selected from fluorinatedhydrocarbons, for example CF₄, CClF₃, CC1₂ F₂, or C₂ F₆, and one kind ofgas selected from the group consisting of Ar, He, Ne, Xe, O₂, and N₂, ina partial pressure ratio of 1: (5 to 100). In particular, in case a gasmixture of CF₄ and one kind of gas selected from the group consisting ofAr, He, Ne, Xe, O₂ and N₂ is employed in a partial pressure ratio of 1:(5 to 100), a good result is obtained.

On the other hand, for the plasma development of lower layer of saidresist layer was employed O₂ or a mixture of O₂ and one kind of gasselected from the group consisting of Ar, He, Ne, Xe and N₂ in a partialpressure ratio of 1:1 to 10.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 and FIG. 2 are the flow charts illustrating the first embodimentof plasma development of double layer resist films according to thepresent invention.

FIG. 3 and FIG. 4 illustrate the second embodiment of plasma developmentof triple layer resist films according to the present invention.

FIG. 5 illustrates the third embodiment of plasma development accordingto the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is explained by the examples below.

EXAMPLE 1

On a silicon wafer was applied polyimide by spinner coating to form athin film of polyimide having a thickness of 1 μm. After the thin filmwas dried, a mixture of poly(glycidyl methacrylate) anddimethyl-diphenylsilane in a volume ratio of 5:1 was applied thereoninto a thickness of 0.2 μm to form a double layer resist film.

The resist film was irradiated with an electron beam of accelerationvoltage 20 kV in 5×10⁻⁶ C./cm².

This was brought into contact with a plasma of gas mixture consisting ofoxygen and CF₄ (volume ratio 3:1, total pressure 0.5 Torr) and held for4 minutes under the electric power of 100 W, so that at the irradiatedpart the upper layer film of 300 Å was left behind and at thenon-irradiated part the lower layer film was exposed.

This was developed with an oxygen plasma (pressure: 0.5 Torr, electricpower: 400 W), so that only the part not covered with the upper layerfilm was selectively developed to form a negative type resist patternhaving a thickness of 1 μm.

From this result the residual film ratio was 83%.

The similar experiments in which the material of lower layer wasreplaced with poly(methyl methacrylate), polystyrene, polyisoprene, orpolystyrene made by plasma polymerization, were carried out, and inevery case the same result was obtained.

EXAMPLE 2

A silicon wafer was applied with polystyrene by spinner coating into athickness of 1 μm, and after being dried was placed on a electrode plateof earth side in a vacuum vessel having a couple of parallel-plateelectrodes, which was then evacuated into 10⁻⁴ Torr. After that amixture of 1-chloro-2-butene and hexamethyldisilazane was made flow into give their each partial pressure up to 0.1 Torr, and then ahigh-frequency electric power of 20 W was impressed between theelectrodes to start discharge and plasma polymerization. After theplasma was held for 1 minute, on the polystyrene film was formed aplasmapolymerized film having a thickness of 0.06 μm.

The resist layer was irradiated with an electron beam of 2×10⁻⁵ C./cm²,and thereafter heated in vacuum at 150° C. for 30 minutes. After that itwas developed in the same process as Example 1.

In the result a negative resist pattern was obtained in a residual filmratio of 95%.

EXAMPLE 3

A silicon wafer was placed on a electrode plate of earth side in avacuum vessel having a couple of parallel plate electrodes, which vesselwas evacuated into 10⁻⁴ Torr, and thereafter into which styrene gas wasintroduced to keep the total pressure at 0.2 Torr. The system was heldunder the electric power of 30 W for 10 minutes, so that a polymer filmhaving a thickness of 0.75 μm was obtained. In succession into thevacuum vessel was introduced diallyldimethylsilane to keep the totalpressure at 0.1 Torr, and was subjected to plasma polymerization underthe electric power of 10 W for 2 minutes to form a polymer film of 0.05μm on the plasmapolymerized styrene film.

The resist layer was irradiated with an electron beam of 2×10⁻⁵ C./cm²,and thereafter was developed in the same process as Example 1, so that anegative type resist pattern was obtained in a residual film ratio of94%.

EXAMPLE 4

On a glass plate coated with vapor deposited chrome was formed aplasma-polymerized styrene film having a thickness of 0.5 μm in the sameprocess as Example 3, and further thereon was formed a thin film of amixture of poly(methyl methacrylate) and triethyl aluminium in a weightratio of 10:1. The film has a thickness of 0.05 μm.

A pattern was drawn by an electron beam of 1×10⁻⁴ C./cm², and thereafterthe upper layer was developed with a plasma of mixed gas of carbontetrachloride and oxygen, while the lower layer was developed withoxygen plasma.

A negative type pattern was obtained in a residual film ratio of 90%.

As explained above, by the method according to the present invention theresidual film ratio of resist film in the plasma development can begreatly improved, so that a pattern having a thickness sufficient to beused for selective etching can be formed.

EXAMPLE 5

For the substrate 1 shown in FIG. 5 was employed a glass plate coatedwith vapor deposited chrome, and said substrate 1 was placed in a plasmagenerating apparatus of high-frequency wave parallel plate electrodetype. Then styrene was made flow into the apparatus in a flow rate of 10cc/min. The gas pressure was kept at 0.15 Torr and a discharge was heldunder a discharge power of 50 W for 20 minutes. A polystyrene layer(lower layer 2) having a thickness of 1.1 μm was formed on the substrate1 (FIG. 5 (A)).

After evacuating the same apparatus, a gas mixture of allyl glycidylether and tetramethylsilane in a volume ratio of 1:1 was introduced intothe apparatus. The inner pressure was kept at 0.2 Torr and plasmapolymerization was held under a electric power of 10 W for 20 minutes.Thus the upper layer 3 was formed (B), having a thickness of 0.1 μm.After drawing a pattern on the double layer resist by an electron beam 4of 1×10⁻⁷ to 1×10⁻⁵ C./cm² (C), the upper layer was developed with amixed gas plasma of CF₄ /O₂ 1:1 in a plasma etching apparatus ofparallel plate electrode type (D). Here the discharge was stopped aftergenerating the plasma under a electric power of 100 W for 3 minutes, andthe reactor was evacuated. Thereafter the plasma development of thelower layer 2 was carried out under the conditions of 0.5 Torr of O₂,100 W and for 10 minutes (E). In case the electron beam dose was morethan 5×10⁻⁶ C./cm², all the lower layer 2 of the part irradiated withthe electron beam was left behind and that of the non-irradiated partwas removed to form a negative type pattern. On the other hand, in casethe electron beam dose was less than 4×10⁻⁶ C./cm², no pattern wasformed.

EXAMPLE 6

Using a silicon wafer for the substrate 1, a double layer resist wasformed in the same process as Example 5 (FIG. 5 (A),(B)). However, theplasma polymerization of the upper layer 3 was conducted using a gasmixture of glycidyl methacrylate and tetravinylsilane in a ratio of 1:1,and under the conditions of the gas pressure 0.12 Torr, discharge power5 W and discharge time 2 minutes. Further, under the same conditions asExample 5 were carried out respectively the electron beam drawing (C),the upper layer development (D) and the lower layer development (E), andthen a negative pattern was formed in 1×10⁻⁶ C./cm² or more.

EXAMPLE 7

On a substrate of silicon wafer the plasma-polymerization of methylmethacrylate was carried out under the conditions of the gas pressure0.2 Torr, electric power 80 W and for 30 minutes. Thereafter a gasmixture of butadiene monoxide and hexamethyl-disilazane in a mixingratio 3:1 was polymerized with plasma under the conditions of the gaspressure 0.3 Torr, electric power 20 W and for 3 minutes. Here thethickness of lower layer 2 was 1.3 μm, while the thickness of upperlayer 3 was 0.2 μm (FIG. 5 (A),(B)).

Further, the electron beam drawing (C) and the developments ((D), (E))were carried out in the same way as Example 5, and the sensitivity ofdouble layer resist was 4×10⁻⁶ C./cm². Besides, in case after theelectron beam drawing in the same condition the substrate was heated at150° C. for 30 minutes (a step between (C) and (D)), the sensitivityupon the development was 2×10⁻⁶ C./cm².

EXAMPLE 8

A silicon wafer (substrate 1) was applied with polyimide by spin-coatingto form a lower layer 2 of polyimide having a thickness of 1 μm (FIG. 5(A)). The upper layer 3 was formed in the same way as Example 2 (B) andafter irradiation with far ultraviolet rays of 20 mJ (C) was developedwith plasma in the same way as Example 1 ((D), (E)). However, thedeveloping time of the lower layer was 30 minutes. Then only at theexposed part was left behind completely the polyimide layer (lower layer2 of (E)) and a negative type pattern was formed.

EXAMPLE 9

In the same process as Example 3 a plasma-polymerization film of styrenehaving a thickness of 1 μm was formed on a silicon wafer, and thereon aplasma-polymerization film of tetramethyl-disiloxane was formed, andfurther thereon a plasma-polymerization film of methylisopropenyl ketonewas formed to make up a resist film having a three layer structure asshown in FIG. 4. The respective condition and film thickness are shownin Table 1 below.

                  TABLE 1                                                         ______________________________________                                                         Upper Middle    Lower                                                         layer layer     layer                                        ______________________________________                                        Conditions of                                                                            Pressure    0.10    0.10    0.20                                   plasma     (Torr)                                                             polymerization                                                                           Electric power                                                                            30      50      30                                                (W)                                                                           Time        5       0.5     15                                                (min)                                                                         Film thickness                                                                            0.20    0.04    1.05                                              (μm)                                                            Conditions of                                                                            Gas         O.sub.2 O.sub.2 + CF.sub.4                                                                    O.sub.2                                plasma     Pressure    0.5     0.5     0.2                                    development                                                                              (Torr)                                                                        Electric power                                                                            100     100     200                                               (W)                                                                ______________________________________                                    

On the resist film a pattern exposure was made by irradiating with 500mJ/cm² of far ultraviolet rays through a chrome mask.

This was developed in the following order: the upper layer 6 wasdeveloped with an oxygen plasma; using the pattern obtained for the maskthe middle layer 5 was developed with a gas mixture plasma of oxygen andCF₄ ; using the resulting pattern of middle layer for the mask the lowerlayer 4 was developed with an oxygen plasma; and finally a positive typeresist pattern as shown in FIG. 4G was obtained. The respectivedeveloping condition is shown in Table 1.

In this case the residual film ratio was 78%.

We claim:
 1. A method for forming fine resist patterns comprising thesequential steps of:(1) forming a lower layer on a substrate byplasma-polymerizing at least one member selected from the groupconsisting of the following monomers (e) to (i):(e) ethylene, propylene,butene, butadiene and isoprene: (f) vinyl chloride, vinylidene chloride,chloroprene, vinylidene fluoride, tetrafluoroethylene, trichloroethyleneand tetrachloroethylene; (g) styrene, chlorostyrene, α-methylstyrene,chloromethylstyrene, brominated styrene and iodinated styrene; (h)methyl methacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, phenyl methacrylate, methyl acrylate, vinyl acetate,methyl vinyl ketone, methyl isopropyl ketone, phenyl isopropyl ketone,phenols, ester compounds, ether compounds and epoxy compounds; and (i)amides, imides, acrylonitrile and methacrylonitrile; (2) forming anupper layer on the above lower layer by plasma-polymerizing thefollowing mixture (k):(k) a mixture of at least one organosiliconcompound with at least one monomer selected from said monomers (e) to(i), said upper layer and said lower layer forming a multilayer film,which multilayer film can be developed, to form a pattern, by a plasmaafter patternwise exposure of the multilayer film to light or radiation;(3) patternwise exposing the multilayer film to irradiation by a lightor a radiation; (4) exposing the upper layer, after said patternwiseexposing, to plasma development in an atmosphere of gas mixture of afluorinated hydrocarbon and a gas selected from the group consisting ofAr, He, Ne, Xe, O₂ and N₂ in a partial pressure ratio of 1:(5 to 100);and then (5) exposing the lower layer, after development of the upperlayer, to plasma development in an atmosphere of O₂ or a gas mixture ofO₂ and a gas selected from the group consisting of Ar, He, Ne, Xe and N₂in a partial pressure ratio of 1:(1 to 10).
 2. A method for forming fineresist patterns according to claim 1, wherein the substrate is a siliconwafer or a glass plate coated with vapor deposited chrome.
 3. A methodfor forming fine resist patterns according to claim 1, wherein theplasma development is carried out by the use of a parallel plateelectrode type plasma-generator, a barrel type plasma-generator, a highfrequency inductive coupling type plasma-generator or a microwavedischarge type plasma-generator.
 4. A method for forming fine resistpatterns according to claim 1, wherein the plasma development is carriedout at an electric output of 100 to 300 and a gas pressure of 0.01 to0.5 Torr.
 5. A method for forming fine resist patterns according toclaim 1, wherein the mixture (k) further contains at least one compoundselected from the group consisting of chloromethylstyrene, iodinatedstyrene, butadiene monoxide, glycidyl methacrylate, allyl glycidylether, epichlorohydrin and epibromohydrin.
 6. A method for forming finephotoresist patterns according to claim 1, wherein the upper layer has athickness of 0.1 to 0.2 μm and the lower layer has a thickness of 0.5 to2 μm.
 7. A method for forming fine resist patterns according to claim 1,wherein a step of heating at 100° to 200° C. is inserted between theirradiation of the multilayer film with a light or a radiation and theplasma development for the upper layer.
 8. A method for forming fineresist patterns according to claim 1, wherein the plasma polymerizationis carried out by the use of a high-frequency discharge typeplasma-generator, a microwave discharge type plasma-generator, or aseparative-type plasma generator in which the discharge part andpolymerization part are separated.
 9. A method for forming fine resistpatterns according to claim 1, wherein the plasma polymerization iscarried out at an electric output of discharge of 50 W or lower.
 10. Amethod for forming the fine resist patterns according to claim 1,wherein the plasma polymerization is carried out at an electric outputof discharge of 20 to 1 W.
 11. A method for forming fine resist patternsaccording to claim 1, wherein the organolsilicon compound is at leastone compound selected from the group consisting of silane compounds,siloxane compounds and silazane compounds.
 12. A method for forming fineresist patterns according to claim 1, wherein the organosilicon compoundis selected from the group consisting of tetramethylsilane,tetravinylsilane, vinyltrimethylsilane, divinyldimethylsilane,trivinylmethylsilane, diallyldimethylsilane, tetraethylsilane,tetramethoxysilane, vinyltrimethoxysilane, methyltriethylsilane,hexamethylidisiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane andhexamethylsilazane.
 13. A method for forming fine resist patternscomprising the sequential steps of:(1) forming a lower layer on asubstrate by plasma polymirizing at least one member selected from thegroup consisting of the following monomers (e) to (i):(e)plasma-polymerizable hydrocarbons; (f) plasma-polymerizable halogenatedhydrocarbons; (g) styrene and styrene derivatives; (h)plasma-polymerizable oxygen-containing compounds; and (i)plasma-polymerizable nitrogen-containing compounds; (2) forming an upperlayer on the above lower layer by plasma-polymerizing the followingmixture (k):(k) a mixture of at least one organosilicon compound with atleast one monomer selected from the monomers (e) to (i), said upper andlower layers forming a multilayer film, which multilayer film can bedeveloped, to form a pattern, by plasma after patternwise exposure ofthe multilayer film to light or radiation; (3) patternwise exposing themultilayer film to irradiation by a light or a radiation; (4) exposingthe upper layer, after said patternwise exposing, to plasma developmentin an atmosphere of a gas mixture of a fluorinated hydrocarbon and a gasselected from the group consisting of Ar, He, Ne, Xe, O₂ and N₂ in apartial pressure ratio of 1: (5 to 100); and then (5) exposing the lowerlayer, after development of the upper layer, to plasma development in anatmosphere of O₂ or a gas mixture of O₂ and a gas selected from thegroup consisting of Ar, He, Ne, Xe, and N₂ in a partial pressure ratioof 1: (1 to 10).
 14. A method for forming fine resist patterns accordingto claim 1 or 13, further comprising the steps of forming, on the upperlayer, a plasma polymer film of a ketone compound and, after theirradiation with a light or a radiation and before the plasmadevelopment for the upper layer, exposing the plasma polymer film of aketone compound to plasma development in an atmosphere of O₂ and a gasselected from the group consisting or Ar, He, Ne and Xe.
 15. The methodfor forming fine resist patterns according to claim 1 or 13, wherein thethickness of said upper layer is thinner than said lower layer.
 16. Themethod for forming fine resist patterns according to claim 1 or 13,wherein said upper layer has a lower rate of plasma development thansaid lower layer.